hello suroot,
you are spot on with the US customers. i bought the s3 on ebay and i have the int'l version gt-i9300. yet, i believe the jb upgrade still screwed up my phone just the same. i upgraded it ota and unfortunately the auto upgrade was selected at the time. i personally do not jump right in when the software upgrade is available in fear of all those bugs that needs to be corrected.
oh well..what else can i say?
Actually, you were right to upgrade if you have 4.1.2.
This will interest you but not many people on AF know about it.
Many of the international GT-i9300's have a bug called SDS (Sudden Death Syndrome) of which, I was one of the first sufferers back in November. The symptom is (often after a nights charge) the phone is completely dead. So dead it gets sent to the carrier or Samsung for a motherboard replacement.
What actually happens is the eMMC (Embedded MultiMedia Card) bricks. This brick is believed to be caused by the wear levelling in the eMMC firmware. Wear levelling is where to spread out the damage of data writes across the memory, it looks at historic data of which blocks have been written to and works out where is the best place to write next, to keep it even accross the card. Anyway, something happens where the firmware finds a bug, something wrong with the data and the entire file system on the eMMC just breaks. The phone OS is gone, everything - gone...
Ok you say, whats this got to do with me?
Well there is a fix, in the kernel of 4.1.2 ROMs. This fix (or work around) changes how the wear leveling works. It detects if you have the faulty eMMC (VTU00M chip with firmware 0xf1 if you're interested) and stops the bad blocks being written to, preventing the phone from dieing. How does this manifest? More often than not... In a freeze..
So, if you have the affected chip and your phone is freezing, you are actually witnessing your phone being protected from SDS. Every time you witness a freeze, if you were on ICS, that would be a new motehrboard. So if you look at it like that, it's not so bad after all.
Some believe that if you let the freezes run their course (dont force reboots etc) that they will be come less frequent, but I don't know.
Anyway to find out a little more about how to check if you are affected and to confirm where it is fixed, see my thread on XDA:
http://forum.xda-developers.com/showthread.php?t=2091045
But there are also more ongoing discussions about the fixes and what they do here:
http://forum.xda-developers.com/showthread.php?t=1993044
Edit > If you're not on 4.1.2 and experiencing freezes and reboots AND have the affected chip, these could be early warnings of SDS